The invention relates to an apparatus for electrolytic surface coating of pourable material, preferably for electrodeposition of metal, in particular aluminum, from an electrolyte. The pourable material is transported in the conveying trough of a vibrator conveyor at least partially in the treatment bath of the electrolyte. The conveying trough forms the two electrodes.
Such an apparatus is known from EP-A 0 209 766.
It is known that by surface improvement of metal parts their life can be lengthened and new areas of use can be opened up. For example, the coating of light metal and ferrous materials may be appropriate, as they generally involve relatively base metals, whose surfaces may corrode under atmospheric action. Suitable pretreatment gives the parts a polished surface without cover layer. The metallic coating can be supplemented with an aftertreatment.
During the electrodeposition, the pourable small parts must be held together so that each individual part has electric contact. On the other hand, the bulk material to be treated should be spread out to the extent that the metal deposition can occur on a product surface as large as possible and that on all parts a current density as uniform as possible is ensured. Another essential prerequisite for satisfactory metal coatings with a uniform layer thickness is sufficient mixing of the material during the electrodeposition. The apparatus for electrolytic surface coating is equipped with conveying means for the transport of the bulk material through the electrolyte which permit, in conjunction with respective inlet and outlet locks, either continuous or intermittent proportioned feeding and discharge of the material. In addition, the movement through the electrolyte and the thorough mixing of the material as well as the transport through the electrolyte must be carried out in such a way that gentle treatment of the material is ensured and even delicate parts are not mechanically damaged during the electrodeposition.
For mass electrodeposition, in particular for electrodeposition of aluminum, a known apparatus is suitable in which a vibrator conveyor with a horizontal and a vertical vibration component is provided for transporting the pourable material. This vibrator conveyor transports the pourable material, utilizing the forces of gravity, in a spiral conveying trough in ascending direction about a central pipe connected with the conveying trough. The vibrator conveyor is lodged with the central pipe in a gasproof vessel containing an electrolyte into which the vibrator conveyor dips partially. As drive means are used for example oblique-action vibrators or obliquely set rods. Such vibrator conveyors require relatively little drive force and permit gentle conveyance of the pourable material. One obtains intensive product movement and good electrolyte exchange as well as a uniform current consumption over the total effective surface of the spread-out material (DE-OS 35 24 510).
Since during coating the material is removed from the anodes and deposited on the bulk material, the anodes must, as is known, be replaced after a predetermined number of hours of operation. Further it is desired to obtain a high material utilization of the anodes, and in addition the availability of the installation is to be maintained by reducing the down times for changing the anodes.
For electrolytic surface coating of pourable material, in particular for electrodeposition of aluminum in a vibrator conveyor system, the anodes may be disposed, accessible from the outside, on the inner wall of the vessel or on a so-called anode shaft cover. As the anodes are being used up by the coating process, their life is limited to a predetermined number of hours of operation. For this reason they are replaced when about 60 to 70% of their material is used up. This is necessary because otherwise the anodes may, in case of irregular erosion, corrode through and the remaining stumps may warp due to their dead weight and thus make a shortcircuit to the cathode. For anode change the installation filled with electrolyte at about 100.degree. C. must be cooled, emptied, flushed with toluene, and dried. The electric leads of the anodes are disconnected, the anodes exchanged through openings in the vessel wall, and for restarting the apparatus these operations take place in reverse order.